The present invention relates to an apparatus and a method for electrolyte injection. The invention relates to an apparatus and a method for efficiently injecting electrolyte through a small hole on a battery case or a top cover after the cover is mounted on the battery case where a battery element is accommodated, and in particular, to an apparatus and a method for injecting electrolyte suitable for injection of electrolyte to a nonaqueous electrolyte battery such as lithium ion battery.
As power source for small size electronic devices, various types of batteries are used. As the power source for the devices such as handy phone, notebook-sized personal computer, cam-corder, etc. nonaqueous electrolyte secondary battery such as lithium ion secondary battery, i.e. small-size large-capacity sealed battery, is used. As the nonaqueous electrolyte battery, cylindrical type and rectangular type batteries are generally used.
The lithium ion battery, used as a power source for small size electronic devices, is produced as follows: Active materials are coated on each of a positive electrode current collector and a negative electrode current collector. The positive electrode and the negative electrode thus produced are laminated with a separator interposed between them, and this is wound up to form a battery element, which is then accommodated in a battery case and sealed.
FIG. 4 shows the drawings to explain assembling process of the battery.
As shown in FIG. 4(A), the battery element is accommodated in a battery case 41. On an open upper portion of the battery case 41, there are provided an external electrode leading terminal 44, an electrolyte injection hole 43, and a top cover 45 with a pressure release valve to prevent rupture of the battery when the pressure inside the battery is increased, and these are mounted on the battery case by means such as laser welding. As shown in FIG. 4(B), an injection nozzle 47 of an electrolyte injection apparatus 46 is airtightly retained on the electrolyte injection hole 43 on the top cover 45. Exhaust means 49 of the electrolyte injection apparatus 46 is driven and an exhaust valve 50 is opened. Then, the air in the battery case is drawn out to attain a predetermined degree of reduced pressure. A predetermined amount of electrolyte 53 is then injected to an electrolyte pot 51 via an electrolyte feeding valve 56 by electrolyte feeding means 55. After injecting the predetermined amount of electrolyte, the electrolyte feeding valve 56 is closed.
Next, as shown in FIG. 4(C), the exhaust valve 50 is closed, and the electrolyte injection valve 52 is opened. Then, the electrolyte in the electrolyte pot 51 is injected into the battery case due to the pressure difference between air pressure in the battery case and the atmospheric pressure applied on a vent hole 57 of the electrolyte pot. After the electrolyte is injected into the battery case, a metal piece is mounted on the electrolyte injection hole, and the injection hole is welded for sealing.
In case of a lithium ion secondary battery, the battery element accommodated in the battery case is produced as follows: A negative electrode material such as carbonaceous material, on which lithium can be doped or undoped, is coated on a band-like current collector and a negative electrode is prepared. A positive electrode material such as lithium transition metal composite oxide, e.g. lithium cobaltate, lithium manganate, etc. is coated on a band-like current collector, and a positive electrode is prepared. These negative and positive electrodes are laminated with a separator interposed between them, and this is wound up to form a battery element.
In the battery case with the battery element accommodated in it, a large number of small voids are formed. Even when the air in the internal space of the battery case has been drawn out, long time is required for completely exhausting the voids. Further, some time is required until the nonaqueous electrolyte is permeated into the battery element, and it is very difficult to inject the electrolyte within short time.
In the method as described above, the driving force for the injection of the electrolyte into the battery case is the pressure difference caused by the reduced pressure, and it does not reach the level of more than one atmospheric pressure.
JP-07099050(A) describes an apparatus, comprising a battery arranged in a chamber and with an electrolyte to be injected into it, and a predetermined amount of electrolyte is filled in an electrolyte reservoir mounted on the injection nozzle. Then, the pressure in the chamber is reduced, and gas such as the air in the electrolyte or the battery element is removed. Then, the pressure is restored to the atmospheric pressure, and pressure is applied again, and the electrolyte is injected.
In this apparatus, however, a funnel-like member with a reservoir corresponding to the amount of the electrolyte to be injected is mounted while the top portion of the battery base with the battery element is opened, and the space inside the battery case is exhausted. A part of the electrolyte is injected into the battery case before exhausting and is permeated into the battery element. As a result, the exhausting from the voids in the battery element is insufficient because of the presence of the electrolyte. Exhausting is performed while the electrolyte is present in the reservoir, which comprises a funnel-like member on the top portion of the battery case, and the pressure is applied as the atmospheric pressure. As a result, air bubbles are generated when the air passes through the funnel-like unit from inside the battery case, and these air bubbles are sent into the battery.
Also, this apparatus is applied to the battery assembling process to inject the electrolyte before the top cover is mounted on the top portion of the battery case. This cannot be applied to the method, in which the electrolyte with higher viscosity is injected through small electrolyte injection hole of less than 1 mm in diameter of a small rectangular type battery as arranged on the top cover on the open upper portion of the battery case.
It is an object of the present invention to provide an electrolyte injection apparatus, by which it is possible to quickly fill the electrolyte to all corners inside the battery case. It is another object of the present invention to provide an apparatus and a method for injecting the electrolyte, by which the electrolyte can be easily injected even in case of a small size rectangular battery.
The present invention provides an electrolyte injection apparatus for injecting an electrolyte into a battery case tightly closed except an electrolyte injection hole, said apparatus comprising an electrolyte injection nozzle airtightly mounted on the electrolyte injection hole, exhaust means for exhausting the space inside the battery case with the electrolyte injection nozzle mounted on the electrolyte injection hole, an electrolyte pot connected to the electrolyte injection nozzle via an electrolyte injection valve and for storing the electrolyte to be injected into the battery case, and electrolyte feeding means for feeding a given amount of the electrolyte into the electrolyte pot via an electrolyte feeding valve, and pressurized gas feeding means for injecting the electrolyte in the electrolyte pot under pressure into the battery case.
Also, the present invention provides the electrolyte injection apparatus as described above, wherein there is provided pressurizing means for preventing deformation of the battery case by applying pressure on wall surfaces of the battery case when the pressurized gas is fed to the electrolyte pot via the pressure valve from the pressurized gas feeding means.
Further, the present invention provides an electrolyte injection method for injecting electrolyte into a battery case tightly closed except an electrolyte injection hole, said method comprising the steps of exhausting internal space of the battery case to a predetermined degree of reduced pressure, storing a predetermined amount of electrolyte in an electrolyte pot, feeding a pressurized gas into the electrolyte pot at the same time or after the starting of the injection of the electrolyte of the electrolyte pot into the battery case, and injecting the electrolyte under pressure into the battery case.
Also, the present invention provides the electrolyte injection method as described above, wherein deformation of the battery case is prevented by applying pressure on wall surfaces of the battery case when the electrolyte is fed under pressure by the pressurized gas.